using multiple primitive colliders instead of mesh collider for an arc?

I have a game that is going to be intended for mobile devices, so I'm trying to keep it light. The game involves a ball rolling around, sometimes very quickly. Because of some shortcomings in the physics with spheres rolling from one plane to the next (examples here, and here), I have been reduced to figuring out how to keep my ball from skipping AND from clipping through walls.

Currently, My timestep is at 0.01333 (75 fps which is far too high though the game is relatively simple), and my default contact offset is 0.0016.I've tried to use DontGoThroughThings, but It gave me very bizarre results where the ball would slow down and then accelerate again.

The solution I've come up with is to use Box Colliders since they will perform much faster than a mesh collider, and tests so far have proven successful for clipping cases. This would be all well, but my problem is some of the modular parts I'm using are 180 degree turns where the wall is a smooth arc, thus my problem with using box colliders.

Main Question: If my 180 arc is 120 tris, would it be more efficient (and less likely to clip) using 8-12 Box colliders to substitute the mesh collider?

I know this varies by many other things going on, but is there a point where no matter what using primitives is worse for the performance?